1. Field of the Invention
The present invention relates to a process of preparing a novel supported Ziegler-Natta catalyst and catalyst system useful for polymerizing or copolymerizing .alpha.-olefins. In one embodiment, the supported Ziegler-Natta catalyst of the present invention is obtained by contacting a particulate functionalized olefin copolymer support with an organometallic compound, complex or mixture thereof under conditions effective to prepare a catalyst precursor material; washing the catalyst precursor; optionally, contacting the washed catalyst precursor with an alcohol; and then contacting that product with at least one transition metal or transition metal-containing compound to obtain the supported catalyst. In another embodiment, the washing step is omitted and the unwashed precursor material is contacted with an alcohol.
A highly preferred organometallic compound employed in the present invention is a combination of an alkyl magnesium compound or complex and an alkyl aluminum halide compound. Supported catalysts prepared in accordance with the process of the present invention exhibit high catalytic activity as well as produce polymers which have improved physical properties which are hereinbelow described.
2. Description of the Prior Art
Ziegler-type catalysts, which usually include components of a metal of Group IV-VIB and organometallic compounds of Groups I-IIIA of the Periodic Table of Elements, are widely utilized in the polymerization of olefins. These catalysts are known to effectively promote the high yield polymerization of olefins possessing commercially desirable characteristics. However, the use of conventional Ziegler-type catalysts are subject to important failings. Thus, new and improved catalysts are continually being sought and developed.
One such improvement comprises supporting the above-identified Ziegler-type catalyst components on refractory inorganic oxide supports, such as SiO.sub.2, Al.sub.2 O.sub.3 and MgO. These supports are available in variety of particle sizes and porosities. Ziegler-type catalysts supported on inorganic oxides oftentimes exhibit high catalytic activity and enhanced polymeric properties compared to Ziegler-Natta catalysts that are unsupported. An example of a catalyst which employs silica as a support material is described in U.S. Pat. No. 4,950,631 to Buehler et al. Increased activity of such silica supported catalysts can be achieved by adding one or more cocatalyst components or promoters to the solid catalyst component.
Despite their usefulness, inorganic oxide supports have certain drawbacks. For example, inorganic oxide supports must generally be calcined at high temperatures or chemically treated with appropriate reagents to remove physically adsorbed water from the surface of the support. The presence of water on the surface of inorganic oxide supports is well known in the art as being a catalytic poison which can adversely affect the catalytic activity of the catalyst.
In addition, inorganic oxide supports have a limited maximum pore size which also can restrict the catalytic performance of the catalyst. Although large pore size inorganic oxides are available, these materials may be friable and the use thereof as catalyst supports may, through attrition, lead to the formation of unwanted fine particles.
Furthermore, it is well known in the art that inorganic oxides adsorb not only water, but other commonly occurring catalyst poisons, such as oxygen, as well. Thus, great care in handling and preparing inorganic oxide supported catalysts must always be exercised.
To circumvent the above drawbacks commonly observed in inorganic oxide supported catalysts, many research groups have focused on substituting polymeric supports for inorganic oxide supports. See, for example, U.S. Pat. Nos. 4,098,979; 4,268,418; 4,404,343; 4,407,722; 4,568,730; 4,900,706; 5,051,484; 5,118,992; and 5,275,993.
Typical polymeric supports employed in the prior art are organic polymers such as polyethylene, polypropylene, polystyrene, polyvinyl alcohol, poly(styrene-divinylbenzene), poly(methylmethacrylate) and the like.
The use of these polymeric supports provides several advantages over similar olefin polymerization catalyst components supported upon inorganic oxides. For example, polymeric supports usually require no dehydration prior to use; they can also be easily functionalized which afford more opportunities to prepare tailor-made catalysts; they are inert; they can be prepared with a wide range of physical properties, via chemical and mechanical means to intentionally give porosity, morphology and size control to the catalyst; and they offer a cost advantage over inorganic oxide supports.
Despite these advantages, prior art polymeric supports nevertheless possess certain inherent disadvantages which decrease their acceptability as viable replacements for inorganic supports. For instance, polymeric supports often lack structural stability at high temperatures and under some solvent conditions. Moreover, the porosity and size of the polymeric support, due to swelling may change drastically over the short time duration required to prepare the catalyst. Furthermore, the choice of the polymer support must be compatible with the polymer produced in order to avoid the formation of gels.
It would thus be highly advantageous to provide a polymeric support which overcomes the above drawbacks while still being useful in the polymerization of .alpha.-olefins.